Balancing supply and demand of electrical energy over time and location is a longstanding problem in an array of applications from commercial generator to consumer. The supply-demand mismatch causes systemic strain that reduces the dependability of the supply, inconveniencing consumers and causing loss of revenue. Since most electrical energy generation in the United States relies on the combustion of fossil fuels, suboptimal management of electrical energy also contributes to excessive emissions of pollutants and greenhouse gases. Renewable energy sources like wind and solar power may also be out of sync with demand since they are active only intermittently. This mismatch limits the scale of their deployment.
Electrochemistry-based technologies offer viable solutions for the storage of energy in an uninterruptible power supply environment. Many types of electrochemical cells have been used for large-scale energy storage. Large-scale electrochemical energy storage devices are valuable for the grid, enabling integration of intermittent renewable energy technologies into base load and performing a variety of electrical services on the conventional grid, e.g., off-peak shifting, load leveling, frequency regulation, to name a few. One type of electrochemical cell is the liquid metal battery in which a pair of electrodes, metal N or its alloy and metal P or its alloy, work in concert as an electron donor (negative electrode) and an electron acceptor (positive electrode), respectively, during discharge. The broad concept of liquid metal batteries has already been disclosed, for example, in U.S. Pat. No. 8,323,816 and U.S. Patent Appl. Publ. Nos. 2011/0014505 and 2012/0104990, which are incorporated by reference herein in their entirety. These cells provide efficient storage capabilities because of the rapid ionic migration and fast, reversible kinetics at both metal electrodes. In a charged state, energy is stored at the negative electrode, which is constituted mainly of a metal, referred to herein as the active metal or anodic metal, at a high chemical potential. In a discharged state, the active metal resides in the positive electrode at a low chemical potential in the form of an alloy. An electrolyte disposed between the two electrodes enables ionic transport of the active metal during charging or discharging.